In general, speech recognition is a series of processes of extracting phonemes, i.e., linguistic information from acoustic information included in speech, and allowing a machine to recognize the extracted information and respond to the recognized information. Conversation in speech is recognized as the most natural and simple method among information exchange media between a large number of human and machines, but there is a restriction that speech of a human should be transformed into codes that a machine can process in order to converse with the machine in speech. The process of transforming the speech of the human into the codes is the very speech recognition.